1. Field of the Invention
The present invention relates to an optical network system, more particularly relates to an optical network system constructed including a plurality of optical route switching nodes having optical route switching functions, still more particularly relates to wavelength path monitoring in an optical network system for confirming and tracking whether a wavelength path specified from one optical transmitting/receiving node forming a transmitting side optical transmitting/receiving end office to another optical transmitting/receiving node forming a receiving side optical transmitting/receiving end office has, as designated, been connected passing through all of a series of optical route switching nodes to be passed through along that wavelength path, that is, “confirmation of connection of wavelength path” and “tracking of wavelength path”.
Here, “confirmation of connection of wavelength path” means basically confirming if each optical route switching node on the wavelength path has correctly performed the routing between the plurality of input ports and plurality of output ports of the node, while “tracking of wavelength path” means basically confirming what sequence a transmitted optical signal has passed through the optical route switching nodes.
2. Description of the Related Art
The scope of application of this optical network system is extremely broad covering for example long distance backbone systems, metro cores, and metro accesses. The network configurations began from the initial so-called “point-to-point” configurations and have grown to so-called ring-type configurations or mesh-type configurations using optical add/drop multiplexing (OADM) nodes or optical route switching nodes for adding/dropping optical signals or switching optical routes without converting optical signals to electrical signals. The realization of such network configurations is making possible use of much more flexible and reliable networks than the past.
Here, an explanation will be given of the related art for the above wavelength path monitoring in such an optical network system. As wavelength path monitoring technology of the related art, the following related art “A”, related art “B”, and related art “C” are known.
(a) The related art “A” is a technique using an optical splitter to take out part of the optical power from a wavelength division multiplexing (WDM) optical signal at each of a plurality of input ports and output ports of an optical route switching node, inputting it to for example an optical spectrum monitor (OSM), measuring the wavelength and optical power of the WDM optical signal, comparing the wavelength at an input port and the wavelength at an output port by the OSM, and confirming that the two match, that is, a technique for wavelength path monitoring utilizing only wavelength information as the wavelength path identifier.
(b) The related art “B” is a technique using an optical splitter to take out part of the optical power from a WDM optical signal at each of a plurality of input ports and output ports of an optical route switching node, using for example a variable optical filter or optical splitter to take out just one wavelength, using a SONET/SDH detector to analyze the content of the so-called J1 byte and J2 byte in the SONET/SDH overhead of the optical signal of the taken out wavelength, and using that analysis for the “confirmation of connection of wavelength path”, that is, a technique for wavelength path monitoring utilizing specific bytes in the SONET/SDH overhead.
(c) The related art “C” is a technique using a specialized pilot tone modulator to superpose a pilot signal as wavelength path information on an optical main signal at the above optical transmitting/receiving node or optical route switching node, using a specialized pilot tone demodulator to detect the pilot signal superposed on the optical main signal as an identifier of the wavelength path at the optical transmitting/receiving node or optical route switching node receiving that signal, and using the pilot signal, differing in amplitude, frequency, or phase for each wavelength of the WDM, as an identifier for “confirmation of connection of wavelength path” for each wavelength, that is, a technique for wavelength path monitoring superposing a pilot signal of a low frequency analog signal on the optical main signal and utilizing this as a wavelength identifier.
The “connection information inside the nodes” acquired using any of the above techniques (prior arts “A”, “B”, and “C”) and the network management system (NMS) are held in advance. If comparing this against the “network configuration information” including the connection information between the nodes and the optical transmission lines (optical fibers) and specifying the path of the optical signal, it is also possible to perform the “tracking of the wavelength path”.
As known publications relating to the present invention, for example, there are Japanese Unexamined Patent Publication (Kokai) No. 2000-69510, Japanese Unexamined Patent Publication (Kokai) No. 8-288905, and Japanese Unexamined Patent Publication (Kokai) No. 2000-183853. Japanese Unexamined Patent Publication (Kokai) No. 2000-69510 discloses use of the light level as the identifier of light in monitoring the optical connection at input/output ports of an optical route switching device (similar to the above prior art “A”), Japanese Unexamined Patent Publication (Kokai) No. 8-288905 discloses an optical cross connect system allocating wavelength as the routing information among the nodes to form an optical network which enables the settings of the optical path to be easily monitored, and Japanese Unexamined Patent Publication (Kokai) No. 2000-183853 discloses a wavelength multiplexed transmission system which enables the normalcy of connection to be confirmed.
Summarizing the problems to be solved in the invention, as the problem in the prior art “a”, as explained in detail later with reference to FIG. 20, in an optical network, if there are different optical transmission lines, there may also be a plurality of wavelength paths of the same wavelength. Therefore, wavelength paths of the same wavelengths may sometimes be simultaneously connected to a plurality of input ports in a single optical route switching node. Accordingly, there is the problem that with just the above wavelength information, it is not possible to discriminate between different wavelength paths having the same wavelength. Further, as shown in FIG. 20B and FIG. 20C, there is the problem that sometimes “error of wavelength path connection” due to “erroneous control of optical path switching” or “erroneous correction between nodes of optical fiber” cannot be detected.
As the problem in the prior art “B”, if once trying to confirm the wavelength path connection information of optical signals, it is necessary to split the optical power and split the wavelength of the WDM signal and input the optical signal to the SONET/SDH detector at each of the input and output ports of the optical route switching nodes and, if increasing the wavelengths, necessary to split the power and split the wavelength further in accordance with the same and lead them to the SONET/SDH detector, so there is the problem that the size of the hardware and the costs of the nodes end up becoming enormous.
Conversely, if trying to confirm the connection of the wavelength path by a single SONET/SDH detector, while the increase in size and costs can be suppressed, there is the problem that a long time ends up being required until finishing confirming the connection of the wavelength path for all of the ports.
As the problem in the prior art “C”, modulators and demodulators especially for the pilot tone become necessary. There is therefore the problem that when the optical network is expanded in size, management of the pilot signal becomes complicated. Further, when individual networks originally comprised of different vendor systems are connected with each other, it is necessary to provide modulators and demodulators for the pilot tone common to the vendors and use common formats. However, when modulators and demodulators for the pilot tone cannot be provided due to hardware restrictions, there is the problem that realization of wavelength path monitoring by the pilot tone becomes difficult.
As the problem “D”, in recent years, construction of an optical network system independent of format which can directly accommodate Gigabit Ethernets (GbE) or 10 GbE optical interfaces at the wavelength of the backbone network is starting to be proposed. When assuming such an optical network system, there is the problem that the format-dependent wavelength path connection confirmation technique using the SONET/SDH overhead such as the above prior art “B” cannot be employed.
As the problem “E” in an NMS arising due to the enlargement of the network scale, as explained above, the wavelength path monitoring is realized by comparing the network configuration information such as the connection information between the nodes and the optical fibers acquired in advance in the NMS and the wavelength path connection information in the nodes collected from the nodes, but if the network is enlarged in scale, the network configuration information to be managed by the NMS and the node internal connection information collected from the nodes also increase. Therefore, there is the problem that the load on the NMS rises and processing time for wavelength path monitoring increases. Also, the efficiency of not only the wavelength path monitoring, but also the overall functions of the NMS are liable to end up being reduced. Further, when newly introducing nodes or when otherwise combining network configuration information by the NMS, there is the problem that even if the connections in a node can be confirmed, the relative connections between nodes are not known, so the “tracking of the wavelength paths” becomes difficult.